Julianne Moore: 'Can we talk about something else now?'

Junkies, porn stars, alcoholics and in her latest film What Maisie Knew a terrible mother – on screen Julianne Moore lets it all hang out. So surely she won't mind Simon Hattenstone quizzing her about all those sex scenes…?

Montauk, New York, final stop on the Long Island Rail Road. Three hours from Manhattan, past the rarefied privilege of the Hamptons, it has that end-of-the-line feel to it: a sleepy, honeysuckled seaside town. This is where kids come to surf, adults to wind down, families to hang. The well-to-do, and the famous, tend to get off the train a few stops earlier. I'm sitting outside an organic cafe waiting for Julianne Moore. All is still and quiet. I'm not sure how Moore fits in here. She's a brilliant actor, who burns up the screen with that shock of red hair and fiery passion.

It would be wrong to say she stars in most of her movies – many of her best films have been epic ensemble pieces, the cinematic equivalent of 10,000-piece jigsaws – but once you have seen Moore, you don't forget her. As the housewife who seals herself off from the world she finds herself allergic to in Todd Haynes's Safe, or as the wife of a closeted gay man in Haynes's Far From Heaven, she brings such brittle intensity to the roles, you can barely breathe watching her. When she does finally crack, it's a sight to behold: nobody sobs from the soul quite like Moore.

Then there's the anger: she's magnificent at rage, famously naked from the waist down in Robert Altman's Short Cuts while arguing with her husband about whether she's kissed another man. In Magnolia, two pharmacists question the lethal mix of drugs she's buying. Her mouth opens, she swallows, then it comes. "Motherfucker! You fucking asshole. Who the fuck… who the fuck do you think you are? I come in here, you don't know who I am, what my life is, you have the balls, the indecency, to ask me a question about my life. Fuck you, too. Don't you call me lady… I am sick!"

And let's not forget sex. While most Hollywood stars are self-conscious, coy or over-actorly in bedroom scenes, Moore simply goes for it, whether as porn star Amber Waves breaking in Dirk Diggler in Paul Thomas Anderson's Boogie Nights, or as the lesbian mother having an away day with Mark Ruffalo in The Kids Are All Right. Moore's characters nearly always have affairs outside marriage. One (admiring) website calls her "Hollywood's go-to gold-star adultress".

Moore in latest film What Maisie Knew.

So I'm sitting outside the cafe, watching the sun-lovers head for the beach, wondering how this tiny seaside town can contain the mighty spirit that is Julianne Moore, when a slight woman in sundress, sunhat and sunglasses walks up. Her arms are bare and fiercely freckled. Her face is fiercely freckled. Moore sits down and we've barely introduced ourselves when she says, "I've got more freckles than just about anybody. My children didn't get them, thankfully. They have tiny little freckles."

It is fair to say that Moore is a little bit freckle-fixated. She has even written a bestselling children's book called Freckleface Strawberry, about a red-haired, freckle-faced little girl. No, she didn't like them as a child, nor did she feel pretty, let alone beautiful. I tell her my older daughter has red hair. "No kidding? Wow! Is she freckly? Does she tan or just stay white?" She wears no makeup, looks pretty if unremarkable and merges seamlessly into the family-friendly, beach-bum environment.

Moore assumes I've come from New York to see her. That's a long way, she says. I tell her I've come from London. She is shocked, and says she'd better get me some food then. So we head into Joni's Kitchen, where she recommends the Grateful Veg: organic seasonal veg, tofu or chicken stir-fry with brown rice. Before I can get out my wallet, she's paid. We head back out into the shade, where she starts telling me her 15-year-old son Cal has got his own band and now takes the bus into the city by himself, while her 11-year-old daughter Liv has done the voiceover for the app of Freckleface Strawberry. She stops talking and looks at my plate. "You're going to need a knife and fork," she says. Before I can get to my feet, she's fetched them.

In her new film, an adaptation of the Henry James novel What Maisie Knew, we observe shocking parental behaviour from the perspective of a little girl. Moore plays Susanna, a needy, narcissistic rock star who's split from her husband and taken a lover. She is monstrously selfish: at times, she worries that she'll lose her daughter Maisie to the boyfriend, at others that she'll lose the boyfriend to Maisie. "She's terrible, right?" Moore grins. "She's so inconsistent, and the one thing kids need is consistency." Actors usually tell you how how much they empathise with their characters. Not Moore. For her, Susanna commits the cardinal sin: she neglects her child. "Look, every working parent is struggling with balancing life and work, but that character is abusive."

Moore and her second husband, the film-maker Bart Freundlich, have brought up their children in New York: summer holidays in Montauk, the rest of the year in the city. The golden rule, she says, has been to put the kids first; to shape work around their needs. "They've both gone to the same school since they were in kindergarten." That must be unusual in the acting world. "It's, erm, challenging. You know, we've managed it."

Her own childhood couldn't have been more different. She was born at the Fort Bragg army base in North Carolina; her father began as a paratrooper and ended up as a military judge, and the family went from city to city following his job. How many schools did she go to? "Nine?" she says uncertainly. When she was 16, they moved to Germany, where she attended Frankfurt American High School.

Far From Heaven: 'I love that movie. It was meaningful for me because Todd [Haynes] wrote it for me, and I was pregnant with my daughter.' Photograph: Allstar/Cinetext/USA FILMS

Was it hard to make friends? "Oh yeah. It's easier when you go into a military environment because the kids are in the same boat. In a community where people have been there for a while, they aren't as friendly: it takes them time to warm up to you. So I say to my kids, if there's a new kid, you go over and include them, and let's invite them over."

Moore has said her peripatetic childhood taught her a good deal about herself and human nature: how we change our behaviour according to our environment. She escaped into books. "My mother brought us to the library every week and I read a lot. That's what kept me company. I went from school to school, but there was always reading." When she started acting at school, that became another means of escape into different worlds.

Moore might have found her childhood destabilising, but she adored her family and is very proud of her parents. They married young, had children early (Julianne and her younger sister and brother), worked, then went to university, becoming the first in their families to do so. Her mother died four years ago and you sense Moore is still devastated. "Mum was only 68… only 20 years older than me. I didn't expect her to die. You think: we're going to be old ladies together." She stares into her smoothie and comes to a stop.

"You know," she says out of nowhere, "I'm British now." All bright again, she tells me how she claimed dual nationality. Her mother moved from Scotland to America aged 10, and when she married Moore's father, she had to renounce her nationality and swear allegiance to America. "I remember she was 27 and came home with an American flag in her hand, crying. She was so upset. I would have been six. My father was applying for law schools and you couldn't be married to a foreign national." Moore has always felt partly British: "I feel my mother became a citizen under duress, and she never let us forget that we weren't fully American. She'd say, 'You're not American, you know? You're only half American.' She was very Scottish."

Moore claimed her British passport as belated justice for her mother? "Yes. She'd have been so happy." Moore has just written a second children's book, My Mom Is A Foreigner But Not To Me.

As we talk, a little girl dressed as a mermaid passes on her way from the beach. Moore smiles at her. "It's hard to walk when you're a mermaid, right? How do you walk with that tail?"

"I have legs," the girl says.

"Oh, I didn't realise you had legs," Moore says.

Montauk's full of surprises. I mention a shop I passed with a rude name: You Got Wood. "I hate that," Moore says. "It's so offensive. I saw it the other day and I'm like, ugh!… Bye, Mermaid, you look so great!… I had to explain it to my daughter. I said, 'Do you know what the expression means?' She said, 'No.' I just gave her euphemisms for erections. Don't make me say them."

Is she incredibly polite?

"Well, yeah. Yeah. That's a nice way to be, right?"

"How weird that you are this polite, stable…"

"…regular," she adds.

"And yet you play these absolute fruitcakes."

She bursts out laughing. "Yeah, yeah. Yeah!"

What's it all about?

"I'm just pretending."

I don't get it, I say. Has she never been a junkie, an alcoholic, just a little bit bonkers?

"Yeah, that was exhausting, because I had to be in a state of stress in every single scene."

She mentions in passing that she's friendly with Daniel Day-Lewis. Does she become her characters as he does? "I have kids. I can't do that."

Would she have done so before?

"I might have. I was much more indulgent then… You can sit around and be in a mood and take your work home with you. But if you have kids to take care of, you can't do that to them. It's not fair."

Did her acting change after having children?

"I think I became much more efficient. A lot of mothers will tell you that."

Moore is so mumsy, it makes me even more curious about her lack of inhibition as an actor. I want to talk to you about sex, I say.

"Sure, sure, go right ahead," she says warily.

"You do sex very well… on screen, I mean."

"Uhuh." She looks away. "There's no sex in this movie," she says of What Maisie Knew.

"I know. I'm talking about your career in general."

Silence.

"Is that a bad thing to say?" I ask.

"Well, it's a little prurient maybe."

I'm just interested, I say. It's unusual for an actor to seem so natural, relaxed, in sex scenes. "So many seem impersonal and unbelievable, but you look as if you enjoy them." It's meant as a compliment, but it doesn't come out right.

"No. No one enjoys them. It's never comfortable. It's something that you do with a great director, with another actor's help, it's a simulation. It's not anything other than that."

In the past, Moore has said most of her films are made for adults, and she's glad her children are too young to see them. But it won't be long before Cal can watch movies such as Short Cuts and Boogie Nights. How does she feel about that? "I doubt he will be interested," she says dismissively. "You have to remember children are not usually very interested in what their parents do for a living."

But they are great movies. Why wouldn't he want to watch them? She looks horrified, as if processing for the first time the idea that her work is available for public consumption. "There are lots of great movies. They don't have to watch something their mother's in. I don't want them to watch my movies. I don't want them to see me as an actor, ever. I only want them to see me as their mother. That's the only relationship I'm interested in having with them. And I think that's the only relationship they're interested in having with me."

I say it's great she's still making films about women who are sexual, when women over 50 are so often banished from the bedroom in movies.

I ask if she is political. "I think everybody's political. The act of being alive is political. Unless you choose to be a hermit, you're automatically political, because you're part of a community."

In Todd Haynes's film Safe. Photograph: Rex

How would she describe her politics? "I would say I'm pretty liberal." Socialist? "Yeah, yeah. It's difficult in an economy like ours to call yourself a socialist, because we're living in a capitalist society where we all benefit from that. But in terms of where we are going politically, a lot of people would like to see a more equitable distribution. I'd like to see that. What is happening now, and in the UK, where the middle part of the economic strata is getting smaller and smaller, that's not the way most of us grew up. I don't understand how it happened so suddenly; why the upper echelons of society have flourished while other people suffer."

She waves at a passing car. "I think that's my friend. I know it is because we sold them our car."

She's still thinking about playing women teetering on the edge. You know, she says, even that goes back to her parents and how they'd get home from work and discuss the people they had dealt with that day. "My mother was a psychiatric social worker and my father worked in the judicial system, so that was the topic of conversation at dinner time: what somebody did and why. There was always a lot of discussion about behaviour and that's what I'm drawn to, real stories and people. I'm not as interested in fantasy or adventure."

Does she consider herself a risk-taker artistically? "No, you're only brave in the face of something you're afraid of, and I'm not afraid of stories, of emotion, of people. So I don't feel it's risky. I feel it's an exploration of something human."

Moore has been nominated for four Academy awards and not won one. Does that bother her? "Oh, of course I care." Last year she starred as Republican Sarah Palin in Game Change, an HBO TV film. "I won a bunch of stuff for that, and it always feels more fun to win. But at the end of the day, yes, I love to win, but I like having a job more."

Which role most deserved an Oscar? "Oh no, I can't answer that. Nooooooh!" I tell her my vote might go to Far From Heaven. "Oh, I love that movie. And it was meaningful for me, because Todd wrote it for me, and I was pregnant with my daughter, so it was a really nice time. I love it."

If she can't tell me her favourite film, what about her worst? "I'm never going to say that," she says. But a second later she does. "Next is pretty bad." What's that about? "It's about nothing. It's about two hours long! I think I'm an FBI agent in it."

Which of Moore's films did her mum like most? She smiles, and tells me about the TV soap opera she was in at the start of her career. "At the time it infuriated me, but what she really cared about was seeing me as often as possible. So when I was on television, that was probably her favourite, because she could see me all the time. I found that very tedious, of course, I was like, ach, don't you even notice what I'm doing?"

Now, she says, she absolutely understands why her mother loved the soap. At 52, she reckons she has a much better grasp of what matters than she did when she was in her 20s. Back then, she just worked and obsessed about her career. "I do think the one thing ageing allows you is to go, 'Well, I know what I like, I know what I don't like.' And I don't think even 20 years ago I understood that. Certainly not 30 years ago. I didn't invest in my personal life at the time. I didn't know myself or spend any time trying to figure myself out. It takes a long time to figure out what you care about."

Could she summarise in a sentence what that is? There's only one thing that truly matters, she says: family. "All I really care about is staying alive for as long as possible for my children, because I don't want them to have to experience loss."